Vehicle heading error compensation

ABSTRACT

Systems and methods for controlling aircraft obtain at least one of ground-referenced longitudinal movement data of the aircraft and ground-referenced lateral movement data of the aircraft. A round-referenced heading of the aircraft is obtained and a heading error is calculated based on a difference between the ground-referenced heading and a target heading. A lateral movement error value is generated based on at least one of the ground-referenced longitudinal movement data and ground-referenced lateral movement data, and based on the heading error.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to controlling vehicles andin particular to compensating for a heading error of the vehicle whencalculating lateral and longitudinal ground speeds.

Aircraft are typically controlled by controls that adjust a pitch, yawand roll of the aircraft. A difference between the target heading, orthe heading indicated by a pilot's control, and the actual yaw resultsin a heading error of the aircraft. Likewise, a difference between alateral ground speed target and an actual ground speed results in alateral ground speed error, and a difference between a longitudinalground speed target and an actual ground speed results in a longitudinalground speed error. Conventional systems correct the lateral groundspeed error by adjusting the roll of the aircraft and correct thelongitudinal ground speed error by adjusting the pitch of the aircraft.However, these systems may not take into account a relationship betweenthe heading error and the actual lateral and longitudinal ground speeds.Over-compensation or under-compensation of lateral and longitudinalground speeds may result.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, a method for controlling anaircraft includes obtaining at least one of ground-referencedlongitudinal movement data of the aircraft and ground-referenced lateralmovement data of the aircraft. The method includes obtaining aground-referenced heading of the aircraft and calculating a headingerror based on a difference between the ground-referenced heading and atarget heading. The method further includes generating a lateralmovement error value based on at least one of the ground-referencedlongitudinal movement data and ground-referenced lateral movement data,and based on the heading error.

According to another aspect of the invention, an aircraft control systemincludes a flight control computer having a data input to receive ameasured longitudinal movement value of an aircraft, a measured lateralmovement value of the aircraft and a measured heading of the aircraft.The flight control computer also has a data processor configured tocalculate a heading error based on a difference between the measuredheading and a target heading and configured to generate a lateralmovement error value based on the measured lateral movement value andthe heading error.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 illustrates an aircraft according to an embodiment of theinvention;

FIG. 2 illustrates a block diagram of an aircraft control systemaccording to one embodiment of the invention;

FIG. 3 is a diagram illustrating a heading error according to anembodiment of the invention; and

FIG. 4 is a block diagram of a method for controlling a vehicleaccording to an embodiment of the invention.

The detailed description explains embodiments of the invention, togetherwith advantages and features, by way of example with reference to thedrawings.

DETAILED DESCRIPTION OF THE INVENTION

Conventional aircraft control systems fail to take into account thecoupling of a heading of the aircraft with lateral and longitudinalgroundspeed, which may adversely affect aircraft control. Embodiments ofthe invention relate to controlling a vehicle's longitudinal and lateralground speed by taking into account a heading of the vehicle.

FIG. 1 illustrates an aircraft 100 according to an embodiment of theinvention. While FIG. 1 illustrates a helicopter, embodiments of theinvention encompass any other rotary-wing aircraft, VTOL aircraft,thrust-based aircraft (i.e. non-rotor-based), and any other vehiclecapable of controlling a heading, lateral movement, longitudinalmovement, and position of the aircraft. The aircraft 100 includes afuselage 110, a first rotor assembly 120 and a second rotor assembly125. The first rotor assembly 120 rotates to lift and maintain theaircraft 100 airborne. The first and second rotor assemblies 120 and 125together control the pitch, yaw and roll of the aircraft 100. In theembodiment illustrated in FIG. 1, the rotor assembly 120 includes onlyone rotor including multiple rotor blades that rotate on a same plane.However, embodiments of the invention encompass any number of rotorassemblies, including rotor-based systems having multiple co-axialrotors, multiple rotor assemblies that are not co-axial, or non-rotorbased designs utilizing thrust vectoring.

The fuselage 110 houses a pilot 111, physical flight controls 112, and aflight control computer 113. In operation, the pilot 111 physicallymanipulates the physical flight controls 112, which may include a stick,lever, wheel, or any other type of physical control, to generate commandsignals or values for longitudinal movement, lateral movement, yaw andcollective movement of the system 100. The flight control computer 113may interpret positions of mechanical components to generate thecommands, or the flight controls 112 may include sensors or othermechanisms to translate physical positions and movements into electricalsignals that are transmitted to the flight control computer 113.

The flight control computer 113 includes memory, one or more dataprocessors, logic and other circuitry to generate, process, and/ortransmit the command signals or values. The command signals may includea lateral command, a longitudinal command, a yaw command and acollective command to control lateral movement of the aircraft 100,longitudinal movement of the aircraft 100, a rotation of the aircraft100 and collective movement of the aircraft 100. It is understood thatthe longitudinal command corresponds to a forward and backward motion(LONG) of the fuselage 110, and in particular to the lowering andraising of the nose and the tail; the lateral command corresponds to aside-to-side motion (LAT) of the fuselage 110, and in particular to aroll motion of the fuselage 110; yaw corresponds to rotation (YAW) ofthe fuselage 110 to the right or left to change a direction of the noseof the fuselage 110; and the collective command corresponds to theraising or lowering of the entire fuselage 110 simultaneously. Asillustrated in FIG. 1, the heading (H) of the aircraft 100 correspondsto a direction that the aircraft 100 is facing.

The flight control computer 113 may store flight control programs andother electronics that may take into account various environmentalconditions and characteristics of the system 100 to generate the commandsignals. The command signals are transmitted to the rotor assembly 120to control the rotor assembly 120.

While FIG. 1 illustrates controls 112 that are physically manipulated bya pilot 111, embodiments of the invention are not limited to a humanpilot 111 or a pilot 111 located in the fuselage 110. In alternativeembodiments, the aircraft 100 may be controlled by a computer executinga computer program, or the aircraft 100 may be controlled remotely by ahuman or computer controller that is not located in the fuselage 110. Insuch an embodiment, a computer may replace the physical controls 112 togenerate the lateral, longitudinal, yaw, and collective commands.

FIG. 2 illustrates an aircraft control system 200 according to anembodiment of the invention. Pilot control commands are generated by anaircraft control input mechanism 201. The aircraft control inputmechanism 201 may correspond to the physical pilot controls 112 of FIG.1, to a receiver that receives remote commands, to a computer thatgenerates pilot commands or any other mechanism capable of generatingpilot control commands to pilot an aircraft.

The flight control computer 202 receives the pilot control commands andgenerates flight control signals to control heading, lateral movementand longitudinal movement of the aircraft. The flight control computer202 may generate additional commands such as a collective command or anyother desired flight control command. FIG. 2 illustrates a headingcommand (H_(cmd)), lateral movement command (LAT_(cmd)) and longitudinalmovement command (LONG_(cmd)). The flight control commands are providedto a rotor control mechanism 203, which generates rotor blade controlsto control a rotor assembly 204. Embodiments of the invention encompassany type of rotor control mechanism 203 including a swashplate assembly,individually-controlled rotor blade servos or any other mechanism tocontrol the rotor assembly 204 or alternative control methods for VTOLaircraft.

In embodiments of the invention, the rotor control mechanism 203controls the rotor assembly 204 to adjust the yaw, pitch and roll of theaircraft according to the received heading command H_(cmd), lateralmovement command LAT_(cmd) and longitudinal movement command LONG_(cmd).

The aircraft feedback system 205 detects characteristics of the aircraftand provides detected heading, lateral movement and longitudinalmovement information to the flight control computer 202. The aircraftfeedback system 205 may measure the characteristics of the aircraftusing any sensor assemblies or electronics, such as geographicalposition determining devices, motion sensors, accelerometers or anyother devices.

Referring to FIGS. 2 and 3, the heading H0 of FIG. 3 is provided as anexample of a heading target resulting from the pilot control commandsH_(cmd) of FIG. 2. In addition, the longitudinal value LONG0 of FIG. 3is provided as an example of a longitudinal ground speed targetLONG_(cmd) resulting from the pilot control commands LONG_(cmd) of FIG.2. A lateral value is not illustrated in FIG. 3, representing a lateralground speed target of zero (0), or a pilot command LAT_(cmd) for avehicle to have no lateral movement.

As illustrated in FIG. 3, when the detected heading H1 of the aircraftvaries from the heading target H0, the heading error (YAW1) has alateral movement element LAT1 and a longitudinal movement element LONG1.In particular, the heading error YAW1 causes the longitudinal movementto appear to be less than the longitudinal movement command value(LONG1<LONG0) and the lateral movement LAT1 appears to be greater thanthe lateral movement command value, which is zero (0) in the exampleillustrated in FIG. 3.

In conventional systems, if the lateral movement and longitudinalmovement are corrected separately of the heading error, errors mayresult in the movement correction, resulting in too much or too littleadjustment of pitch, roll and yaw.

FIG. 4 illustrates a method according to an embodiment of the invention.In block 401, the heading, longitudinal ground speed and lateral groundspeed of a vehicle, such as an aircraft, are measured, detected, orderived. The heading, longitudinal ground speed and lateral ground speedmay be measured or detected by sensors, by electronics devices such asgeographic position detection systems, global positioning systems or anyother system or method. In addition, the longitudinal ground speed andlateral ground speed may be derived from measured velocities inalternate reference frames and corrected to the ground referenced framevia measured pitch, roll and heading values.

In block 402, a heading error is calculated by determining thedifference between the target heading and the detected heading. Thetarget heading may be provided by a pilot input or other flight controlsystem.

In block 403, a lateral ground speed error is calculated based on theheading error and the detected lateral ground speed error. In addition,the lateral ground speed error may further be calculated based on thedetected longitudinal ground speed.

In one embodiment, the lateral ground speed error value is calculatedaccording to the following equation:v _(err) =v _(tgt) −v cos(ψ_(err))+u sin(ψ_(err)).  (1)

In the above equation (1), v_(err) is the lateral ground speed errorvalue, v_(tgt) is a lateral ground speed target value, v is the detectedlateral ground speed value, u is the detected longitudinal ground speedvalue and ψ_(err) is a value of the heading error.

In block 404, a longitudinal ground speed error is calculated based onthe heading error and the detected longitudinal ground speed error. Inaddition, the longitudinal ground speed error may further be calculatedbased on the detected lateral ground speed.

In one embodiment, the longitudinal ground speed error value iscalculated according to the following equation:u _(err) =u _(tgt) −u cos(ψ_(err))−v sin(ψ_(err)).  (2)

In the above equation (2), u_(err) is the longitudinal ground speederror value, u_(tgt) is a longitudinal ground speed target value, u isthe detected longitudinal ground speed value, v is the detected lateralground speed value and ψ_(err) is a value of the heading error.

In block 405, a heading command, lateral ground speed command andlongitudinal ground speed command are generated based on the headingerror, lateral ground speed error and longitudinal ground speed error.

In block 406, the yaw, roll and pitch of a vehicle are controlled basedon the heading command, lateral ground speed command and longitudinalground speed command. For example, in an embodiment in which the vehicleis a helicopter, a swashplate or individual rotor blade servos arecontrolled, and a tail rotor may also be controlled, to control the yaw,roll and pitch of the helicopter.

In embodiments of the invention, the flight control computer 113 of FIG.1 or 202 of FIG. 2 may perform the calculation and generation operationsof blocks 402-405. In addition, the rotor control mechanism 203 of FIG.2 may control the yaw, roll and pitch of the aircraft. However,embodiments of the invention encompass any computer, computer system ornetwork of computers or electrical devices capable of receivingmeasurements, calculating error values, generating commands to control avehicle and generating vehicle control signals based on the commands.

According to embodiments of the invention, a vehicle, such as anaircraft, is controlled by adjusting the yaw, pitch and roll of theaircraft. The heading is measured as well as the lateral ground speedand longitudinal ground speed. Error values are calculated for each ofthe heading, lateral ground speed and longitudinal ground speed toaccount for differences between a target heading, lateral ground speedand longitudinal ground speed and the detected values. The error valuesof the lateral and longitudinal ground speeds take into account theheading error to account for the coupling relationship between theheading error and the lateral and longitudinal ground speeds.

While an embodiment has been described in FIG. 4 with respect to groundspeed by way of example, it is understood that embodiments of theinvention encompass any ground-referenced motion data, including groundspeed, ground acceleration (i.e., acceleration of a vehicle with respectto the ground), and ground position (i.e., position of the vehicle withrespect to the ground). The ground-referenced motion data may be senseddirectly by sensors, or may be derived from other data. For example,while a ground position may be sensed directly by sensors or a wirelessposition-determining systems (e.g., a global positioning system (GPS)),acceleration and speed may also be derived from sensor data or fromtransforms of heading data, pitch data or any other sensed data.

Embodiments of the invention include methods and systems for generatingerror values and correcting the flight controls of an aircraft. Themethod includes obtaining at least one of ground-referenced longitudinalmovement data of the aircraft and ground-referenced lateral movementdata of the aircraft. In embodiments of the invention, the term“movement data” refers to one or more of position data (i.e., data thatdoes not include speed or acceleration), speed data, acceleration, orany other derivative of acceleration (e.g., changes in acceleration).The method also includes obtaining a ground-referenced heading of theaircraft. A heading error is calculated based on a difference betweenthe ground-referenced heading and a target heading. A lateral errorvalue is generated based on at least one of the ground-referencedlongitudinal movement data and ground-referenced lateral movement data,and based on the heading error.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

What is claimed is:
 1. A method for controlling an aircraft, comprising:obtaining at least one of ground-referenced longitudinal movement dataof the aircraft and ground-referenced lateral movement data of theaircraft; obtaining a ground-referenced heading of the aircraft;calculating a heading error based on a difference between theground-referenced heading and a target heading; generating a lateralmovement error value based on at least one of the ground-referencedlongitudinal movement data and ground-referenced lateral movement data,and based on the heading error; and generating a longitudinal movementerror value based on at least one of the ground-referenced longitudinalmovement data and ground-referenced lateral movement data, and based onthe heading error, wherein the longitudinal movement error value is aground-referenced longitudinal speed error value, and theground-referenced longitudinal speed error value is generated accordingto the equation:u _(err) =u _(tgt) −u cos(ψ_(err))−v sin(ψ_(err)) wherein u_(err) is thelongitudinal ground speed error value, u_(tgt) is a longitudinal groundspeed target value, u is a detected ground-referenced longitudinal speedvalue, v is a detected ground-referenced lateral speed value and ψ_(err)is a value of the heading error.
 2. The method of claim 1, wherein thelateral movement error value is further based on a longitudinal movementerror corresponding to a difference between the ground-referencedlongitudinal movement data and a target longitudinal movement value. 3.The method of claim 2, wherein the lateral movement error value is aground-referenced lateral speed error value, and the ground-referencedlateral speed error value is generated according to the equation:v _(err) =v _(tgt) −v cos(ψ_(err))+u sin(ψ_(err)) wherein v_(err) is theground-referenced lateral speed error value, v_(tgt) is a lateral groundspeed target value, v is a detected or derived lateral ground speedvalue, u is a detected longitudinal ground speed value and ψ_(err) is avalue of the heading error.
 4. The method of claim 1, further comprisinggenerating a lateral movement command signal based on the lateralmovement error value to control a ground-referenced lateral speed of theaircraft.
 5. The method of claim 1, further comprising generating alongitudinal movement command signal based on the longitudinal movementerror value to control a longitudinal movement of the aircraft.
 6. Anaircraft control system, comprising: a flight control computer having adata input to receive a measured longitudinal movement value of anaircraft, a measured lateral movement value of the aircraft and ameasured heading of the aircraft, having a data processor configured tocalculate a heading error based on a difference between the measuredheading and a target heading and configured to generate a lateralmovement error value based on at least one of the measured lateralmovement value and the measured longitudinal movement value, and theheading error, the data processor being further configured to generate alongitudinal movement error value based on at least one of the measuredlongitudinal movement value and the measured lateral movement value, andthe heading error, wherein the longitudinal movement error value is alongitudinal ground speed error value, and the longitudinal ground speederror value is generated according to the equation:u _(err) =u _(tgt) −u cos(ψ_(err))−v sin(ψ_(err)) wherein u_(err) is thelongitudinal ground speed error value, u_(tgt) is a longitudinal groundspeed target value, u is the measured longitudinal movement value, v isthe measured lateral movement value and ψ_(err) is a value of theheading error.
 7. The aircraft control system of claim 6, wherein thelateral movement error value is further based on the longitudinalmovement error value corresponding to a difference between theground-referenced longitudinal movement data and a target longitudinalmovement value.
 8. The aircraft control system of claim 7, wherein thelateral movement error value is a lateral ground speed error value, andthe lateral ground speed error value is generated according to theequation:v _(err) =v _(tgt) −v cos(ψ_(err))+u sin(ψ_(err)) wherein v_(err) is thelateral ground speed error value, v_(tgt) is a lateral ground speedtarget value, v is the measured lateral movement value, u is themeasured longitudinal movement value and ψ_(err) is a value of theheading error.
 9. The aircraft control system of claim 6, wherein thedata processor of the flight control computer is further configured togenerate a lateral movement command signal based on the lateral movementerror value to control a lateral movement of the aircraft.
 10. Theaircraft control system of claim 9, further comprising a rotor controlmechanism configured to receive the lateral movement command signal fromthe flight control computer and to mechanically control rotors of theaircraft based on the lateral movement command signal.
 11. The aircraftcontrol system of claim 6, wherein the data processor of the flightcontrol computer is further configured to generate a longitudinalmovement command signal based on the longitudinal movement error valueto control a longitudinal movement of the aircraft.
 12. The aircraftcontrol system of claim 11, further comprising a rotor control mechanismconfigured to receive the longitudinal movement command signal from theflight control computer and to mechanically control rotors of theaircraft based on the longitudinal movement command signal.
 13. Theaircraft control system of claim 6, wherein the data processor of theflight control computer is further configured to generate a lateralmovement command signal based on the lateral movement error value tocontrol a lateral movement of the aircraft, the data processor of theflight control computer is configured to generate a longitudinalmovement error value based on the measured longitudinal movement valueand the heading error, and the data processor of the flight controlcomputer is configured to generate a longitudinal movement commandsignal based on the longitudinal movement error value to control alongitudinal movement of the aircraft.
 14. The aircraft control systemof claim 13, wherein the lateral movement error value is a lateralground speed error value, the lateral ground speed error value isgenerated according to the equation:v _(err) =v _(tgt) −v cos(ψ_(err))+u sin(ψ_(err)) wherein v_(err) is thelateral ground speed error value, v_(tgt) is a lateral ground speedtarget value, v is the measured lateral movement value, u is themeasured longitudinal movement value and ψ_(err) is a value of theheading error, the longitudinal movement error value is a longitudinalground speed error value, and the longitudinal ground speed error valueis generated according to the equation:u _(err) =u _(tgt) −u cos(ψ_(err))−v sin(ψ_(err)) wherein u_(err) is thelongitudinal ground speed error value, u_(tgt) is a longitudinal groundspeed target value, u is the measured longitudinal movement value, and vis the measured lateral movement value.